The present invention is a method for producing a catalyst for use in the dehydrogenation of ethylbenzene to styrene (a “STYRENE” catalyst), and for the catalyst produced by the inventive method. The catalyst of the present invention comprises a high purity metal and at least one promoter in the form of solid oxides, oxide hydrates, hydroxides, hydroxycarbonates or metals. The catalyst is prepared via a method which comprises the preparation of at least one high purity iron precursor with or without an additional support material and which uses a nominal amount of water in the catalyst production. The catalyst pellets prepared with the high purity metal precursor are essentially free of sulfur and chloride contaminants.
As taught in published U.S. patent application Ser. No. 20010020118, an effective dehydrogenation catalyst contains from about 40 wt % to about 90 wt % iron oxide calculated as Fe2O3, from about 5 wt % to about 20 wt % of an alkali metal compound calculated as an alkali metal oxide, from about 0.1 ppm to about 1,000 ppm of a source of palladium or platinum selected from the group including elemental palladium, elemental platinum, compounds containing palladium, compounds containing platinum and combinations thereof, from about 0.5 wt % to about 10.0 wt % of a molybdenum or tungsten compound calculated as MoO3 or WO3, and from about 4.0 wt % to about 12.0 wt % of a cerium compound, calculated as CeO2, wherein all weight percents are based on the total weight of the catalyst. Additional promoters may be included with the catalyst.
The '118 application also teaches that a most preferable dehydrogenation catalyst contains from about 40 wt % to about 90 wt % iron oxide calculated as Fe2O3, about 5 wt % to about 20 wt % of an alkali metal compound, preferably potassium oxide, about 4.0 wt % to about 12 wt % of cerium oxide calculated as CeO2, about 0.5 wt % to about 10.0 wt % of molybdenum or tungsten oxide calculated as MoO3 or WO3, preferably molybdenum oxide, about 0.2 wt % to about 10.0 wt % of calcium or magnesium oxide, preferably calcium oxide, about 10 ppm to about 1000 ppm of titanium oxide calculated as TiO2, about 100 ppm to about 2000 ppm of chromium oxide calculated as Cr2O3, and about 1 ppm to about 1000 ppm of a source for palladium or platinum, preferably palladium, calculated on an elemental basis. Additional components that can be added to this catalyst include from about 0.1 wt % to about 10.0 wt % of an oxide of aluminum, silicon, manganese, copper, zinc, cadmium, vanadium, and cobalt, calculated on an elemental basis. The dehydrogenation catalysts of the '118 patent are prepared by using one or a combination of the following methods: co-precipitation, decomposition, impregnation and mechanical mixing or any other method, as would be readily appreciated by those skilled in the art. The method chosen should guarantee intimate mixing and uniform distribution of the components.
It is well established in the art that different forms of iron oxide, red, yellow, brown and black, can be used for preparation of the dehydrogenation catalyst. Likewise, it is known in the art that the iron oxides can be derived from a variety of precursor materials, both natural and synthetic, using a number of processes. Generally, iron is added to the catalyst compositions as red iron oxide, α-Fe2O3 (hematite), or yellow iron oxide, Fe2O3H2O (goethite), but others can be readily utilized as would be appreciated by those skilled in the art. Particularly suited are pigment grades of the iron oxides. Ferrites may also be used, such as potassium ferrite.
Precipitated, pigmentary grade iron oxides are generally regarded as superior raw materials for STYRENE catalysts as compared to other types of iron oxides such as natural iron oxides or those prepared by thermal decomposition of ferric nitrate, ferric chloride, ferrous sulfate and the like. However, precipitated iron oxides can have a high cost, the preparation method is labor intensive, and the by-products are deleterious to the environment. Ferric or ferrous sulfate is a preferred iron source for precipitated iron oxides because of availability and economics. But, sulfur contamination can have a deleterious effect on the environment and an adverse impact on the performance of the resulting STYRENE catalyst and process. Further, the precipitation method tends to result in the formation of very viscous and gelatinous iron hydroxide or iron oxyhydrate precursor which can be very difficult to filter and wash.
A common procedure for preparing a precipitated oxide involves treating a solution of an iron salt, such as ferric nitrate, with a base, such as aqueous ammonia or sodium carbonate. The resulting iron oxyhydroxide precipitate is washed and filtered repeatedly to remove salts—ammonium nitrate or sodium nitrate—formed during the precipitation process. The washed filter cake is then dried and calcined. For making a catalyst containing potassium oxide and iron oxide, a mixture of the required amounts of potassium carbonate and unhydrated iron oxide are dry-blended with a small amount of organic lubricant. Water is then added into the oxide mixture to form an extrudable paste which is then formed in cylindrical pellets, dried and calcined at about 600° C.
Supported iron catalysts are usually prepared by impregnating a solution of an iron salt onto a refractory metal oxide such as Al2O3, SiO2, TiO2 or ZrO2. The impregnation can be carried out by incipient wetness techniques or by excess wetting followed by vacuum drying. Supported iron catalysts can have STYRENE activity similar to precipitated iron catalysts on an iron mass basis, but they are typically inferior on a catalyst volume basis and they inevitably suffer from the acidity of the metal oxide supports which increases the selectivity of undesirable methane.
Thus, it would be advantageous to have a method to produce a STYRENE catalyst starting from an iron oxide that has a relatively simple to manufacture, that requires little to no washing steps, that has a relatively low product cost, and that does not generate by-products are deleterious to the environment.